This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. C1 Esterase Inhibitor (C1INH) is a normal constituent of human blood and is one of the serine protease inhibitors (serpins). The protein functions as an inhibitor of the complement and contact systems (intrinsic clotting). Hereditary angioedema (HAE) is manifested by attacks of non-itching swelling of the extremities, face, trunk, airway, or abdominal viscera, occurring spontaneously or secondary to trauma. It is inherited as an autosomal dominant trait and is due to deficient activity of C1INH . Treatment of HAE patients with C1INH has been documented in the scientific literature since the concentrate became available in Europe in the early 1970's. There was no evidence of toxicity. This is a multi-center open-label study that will evaluate the efficacy and safety of C1INH-nf as prophylaxis to prevent HAE attacks. Subjects will be given prophylactic infusions of C1INH-nf every 3-7 days (approximately 1-2 times a week). The infusion schedule will be determined by the investigator based on the subject's response to the therapy. The efficacy will be analyzed by the number of all angioedema attacks that occur during the treatment irrespective of whether the subject obtained open label C1INH-nf or not and will be summarized. For analysis of safety, the number and severity of adverse experiences will be summarized. This study may help develop alternative treatment option for HAE patients.